[opendtv] Re: Twang's Tuesday Tribune (Mark's Monday Memo)
- From: Segal Gary-r36550 <Gary.Segal@xxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 5 May 2004 18:06:22 -0700
> From: opendtv-bounce@xxxxxxxxxxxxx
> [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Mike Enright
> Sent: Tuesday, May 04, 2004 11:15 PM
> To: opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Re: Twang's Tuesday Tribune (Mark's Monday Memo)
>
> IPV6 on the one hand allows for a great many addresses to be
> assigned.
> The address field in IPv6 is 128 bits. On the other hand, and
> ironically, there is the possibility that if two cards with
> the same MAC
> address were in the same site, they could end up with the same
> global-scope IPv6 address. Briefly, the 48-bit MAC address is
> converted
> to a 64-bit interface ID by concatenating a fixed 16-bit
> value and then
> the 64-bit network number is concatenated.
Folks, I'm a little confused here...
IPV6 (and IPV4 for that matter), assign IP addresses, not MAC address. IPV6
has a 48 bit IP address field, while IPV4 has a 32 bit field. IP addresses are
logical, and are assigned to physical devices by a variety of methods (dynamic
assignment by DHCP is currently the most popular method in the data networking
world). IP address assignments are not permanent, and can change as a physical
device moves between networks or sub-networks.
MAC address are supposed to be unique identifiers assigned to the physical
device at manufacture time. For Ethernet devices, the MAC address is 48 bits
(and it has been 48 bits since Xerox invented Ethernet). MAC address are
supposed to be permanent and unchangeable in the MAC device. However, this
rule isn't really true any more as a some systems allow the user to modify
their Ethernet MAC address.
The key difference between an IP address and an Ethernet MAC address is that
the IP addressing systems is designed to support dynamic device address
assignment and changes, while the Ethernet address system is designed to assign
a permanent address to a physical device.
Note that IP protocols have a variety of tools that are used to bind IP
addresses to MAC address (DHCP, ARP, RARP are the three biggies).
MAC address are supposed to be unique, and are assigned by the IEEE (in blocks
to device manufacturers). IP address that are on the public internet are also
supposed to be unique, and are assigned by the IANA (in blocks to network
operators). When devices connect to a network, they are assigned an IP address
from that network's assigned range. Note that private internets can re-use IP
addresses from a few special IP address ranges such as 192.168.x.x. This is
fine as long as these networks are never directly connected to the public
internet.
So, what I'm confused about is if we're discussing MAC addresses or IP address.
-Gary Segal
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